Piston driven internal combustion engines commonly have valvetrains that affect flow into and out of a cylinder. Intake and exhaust valve opening and closing positions, relative to crankshaft position, can be at fixed positions, or alternatively, at positions that vary with engine operating conditions. Typically, for engines having adjustable valve timing, engine operating conditions are used as a basis to adjust valve and spark timing.
One method to adjust engine spark timing for an engine having variable intake valve timing is described in U.S. Pat. No. 6,681,741. After engine starting, this method adjusts spark advance based partially on opening timing of an intake valve. Further, the method describes retarding intake valve timing so that air-fuel mixing may be improved and so that the engine can tolerate spark retard to increase catalyst heating.
The above mentioned method also has a disadvantage. Namely, the method does not account for the fuel injection timing and its affect on the heat of vaporization and spark timing. Therefore, the method does not benefit from of several advantages that may be available as a result of open valve fuel injection.
When fuel is injected to an intake port on a closed intake valve the fuel can form a puddle in the intake port. Opening the intake valve causes at least a portion of the fuel puddle to be drawn into the cylinder, but since the fuel is drawn from a puddle it may be more difficult to vaporize. On the other hand, if at least a portion of the fuel is injected while the intake valve is open then air-fuel mixing and/or fuel vaporization may be improved. As a result, open intake valve fuel injection may provide changes in minimum spark for best torque and/or charge cooling that may permit additional spark advance. Consequently, it can be beneficial to adjust spark timing in response to the effect injection timing has on air-fuel mixing and/or fuel vaporization.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control spark timing for an engine having variable intake valves.